'underpromise' originates from the combination of 'under-' meaning 'below' and 'promise' meaning 'a declaration or assurance.'

'underpromise' evolved from the Old English word 'under' and the Latin word 'promissum,' eventually becoming the modern English word 'underpromise.'

Initially, it meant 'to promise less,' and this meaning has largely remained the same in modern usage.